what would cause the header to glow red

[knight rider]

"update" what would cause the header to glow red

just cleaned the carb on my 03 yz450f and changed out the plug. kicked it over and the pipe stated glowing coming out the head. there was coolant in the radiator so what would cause it to heat up that fast and that hot?

 

[plynn41]

Bike is running lean. Check the setting on your air screw.

 

[whenfoxforks-ruled]

Bike is running rich, check your fuel screw.

 

[Ol'89r]

On a YZF450 it is normal for the head pipe to glow after a few minutes of sitting without air flow through the radiators. If the pipe starts to glow after only a few seconds, you may have leaky exhaust valves.

 

[knight rider]

i will mess with the fuel see what happens

 

[Matt90GT]

The bike is air cooled. dont let it idle for more than a minute on the stand.

 

[knight rider]

The bike is air cooled. dont let it idle for more than a minute on the stand.

it was within seconds it started doing it. hopefully it is something simple.

 

[whenfoxforks-ruled]

Bet you the choke makes it worse/brighter?

 

[plynn41]

Bike is running rich, check your fuel screw.

:laugh: Good one Bob! How many bikes you ever melted down running too rich?

 

[Rich Rohrich]

:laugh: Good one Bob! How many bikes you ever melted down running too rich?

Assuming, as Ol89r correctly pointed out that the exhaust valves are sealing properly a higher than normal exhaust gas temperature is the result of delayed combustion which dumps additional heat into the exhaust system. The most common causes of delayed combustion?

- retarded ignition timing
- too lean a mixture
- too rich a mixture

plynn - If you are going to mock somebody you might want to do some homework so the correct person looks like an ass. ;)

 

[plynn41]

Rich, is this true or not?

High end tuners measure exhaust temperature as a way of determining fuel mixture requirements? I.e., a hot exhaust indicates a lean mixture and a cool exhaust indicates richness. Your post suggests that exhaust temperature can't indicate anything about the jetting because it could be rich or lean.

The writer just cleaned his carburetor--his ignition didn't likely change. And not to be a smart ass to someone who knows what he's talking about, but seriously, have you ever seen a bike melt down from running too rich?

Respectfully,
Lynn

 

[Rich Rohrich]

Rich, is this true or not?

High end tuners measure exhaust temperature as a way of determining fuel mixture requirements?

Not true for anyone that actually knows how to tune. Plug reading and wide band oxygen sensors are the preferred methods by "real tuners"

I.e., a hot exhaust indicates a lean mixture and a cool exhaust indicates richness.

Incorrect. Higher than "normal" exhaust gas temperatures (EGT) indicate late combustion in the cycle. Lean mixtures tend to burn slow and raise the exhaust gas temperatures, overly rich mixtures can burn even slower (to the point of some of the fuel burning in the pipe) and raise the EGT even higher. This rich effect is especially true at low rpm where the combustion tends to be inconsistent at the best of times. Want graphic proof? Leave the choke on longer than you should on a modern four-stroke and the pipe will glow bright enough to be seen from outer space. At WOT and high engine speeds rich mixtures tend to have less impact on EGT so it gets even more unreliable as a means to determine A/F ratio.

Retarding the ignition timing will also raise the EGT. This is a fundamental part of two-stroke tuning. Retarding the high speed ignition timing on a two-stroke will raise the EGT and some of the available combustion heat is manipulate the pipe wave timing and improve the scavenging/ram tuning. Less efficient combustion tends to raise exhaust temperatures, so they are effectively trading off some thermal/combustion efficiency to improve the scavenging and increase the delivery ratio of fresh charge.


So rich mixtures can potentially raise EGT, as can lean mixtures, and ignition advance which is variable at different rpm also has a huge influence on EGT. Don't forget that engine load can also influence it. So you have to ask yourself, when the EGT changed what was the root cause.

I think the critical part that is often times over looked when people try to measure tuning variables with things like EGT is they fail to grasp all of the interactions that contribute to the number they read.

Your post suggests that exhaust temperature can't indicate anything about the jetting because it could be rich or lean.

Given how little time is spent at WOT on an MX bike it's difficult to isolate temp changes in the exhaust based solely on A/F ratio. I really believe that the influence of exhaust timing, and ignition advance/retard make part throttle readings "pretty useless" especially given how slowly most affordable thermocouples respond. Considering the number of throttle transitions you'll see during an average lap around the local MX track it's hard to see a real value in tuning EGT. For karting use where WOT performance plays a greater role EGT seems to hold much greater value as a tuning aid but I still tend not to trust it as anything but a reference based on a previously established and confirmed baseline temperature.

Even in those situations you are just measuring a secondary effect of combustion efficiency with EGT not air/fuel ratio, so ignition timing, charge purity, and a host of other factors will influence the final temps. Wideband O2 sensors feeding a fast DAQ system is IMHO the only proper way to measure A/F ratio without HUGE resources, but it's still an expensive proposition so it's largely ignored by a lot of "tuners"

It's interesting to note that Honda with all it's resources uses a detonation counter system that detects knock intensity and frequency. They developed it as an affordable tool for racers to get optimum engine settings (jetting, ignition timing) without the need of an expert tuner that can read plugs.

I guess they don't think EGT is all it's cracked up to be either. ;)

Here's a little excerpt from a paper Honda published. The full paper has lots of the the pertinent details

From SAE 1999-01-3324 / JSAE 9938079
Detonation Counter for Production Racing Motorcycle
Hajime Soda and Tomonori Sato
Honda Racing Corp.
Copyright © 1999 Society of Automotive Engineers, Inc.

ABSTRACT
When the detonation caused by pre-ignition and post-ignition,
it is generally known that strong vibrations from
the combustion chamber develop from impact of that
combustion pressure. This will affect the engine. Methods
to accurately measure the strength of this detonation and
its usage are being considered and used from various
viewpoints. We measure this detonation quantitatively by
the detonation counter. This is done in order to bring out
optimum performance of the engine, specifically the
spots, carburetor settings, and ignition timing. Where
adjustments must be made and it is useful as a tool for
judging, conducting, and setting adjustment directions
and volume quickly and accurately. Furthermore, simplification
of this system has the enable it to be sold on the
market. As a result of this, it now has spread to and is
being used for racing base.
INTRODUCTION
Increasing the compression ratio, making air fuel ratio
(hereinafter referred to as A/F) lean are generally used
as methods to increase output, and increase fuel savings
for vehicles used for racing. However, these methods
usually increase detonation in the combustion chamber,
as a result this detonation hampers output performance.
The method, which measures strength and frequency of
detonation and assesses abnormal combustion quantitatively,
is being considered from various angles. As the
detonation of internal combustion engines are caused by
many factors, such as air mixture pressure, temperature,
A/F, mixing condition, octane content of fuel, engine
speed (NE), structure of combustion chamber, etc.
Although the detonation is judged accurately, it is not
easy to decide how to set the engine to control the above
noted detonation.
The case of engine for racing engines, the optimum set-ting
of A/F for carburetor, we must consider that the
weather conditions, rider’s engine speed range, throttle
opening range in each circuit, each race, each run. This
is necessary to bring out optimum engine performance.
In the past, the mechanic looked at and confirmed the
burning conditions of pistons and plug, the amount of car-
bon stuck, and damage to the piston head after circuit
running. Then they made a comprehensive judgment of
acceleration of engine speed, traction, burning noise
caused by detonation and information from the rider. This
largely depended on human intuition. As a result, there
are cases of engines not running at the optimum setting,
but rather at a low performance condition. Lap times did
not improve, and there were cases when the engine was
badly affected by frequent occurrence of detonation. This
means that the mechanic (or rider) needs to have a lot of
experience and considerable data, which has accumulated.
In recent years, gasoline used in racing has changed
from leaded to unleaded gasoline. This was due to environmental
protection and lowering octane content of gasoline.
As a result, the generation limit of detonation was
lowered and the number of reported cases of burn have
increased.
We want to reduce the load to the mechanic and to the
rider by making feedback of techniques, setting methods
of 500cc racing motorcycle on the market, and relating to
detonation developed by factory activities, as much as
possible. Detonation counter was developed as a tool to
set the engine at optimum condition that does not depend
on human intuition. The detonation counter indicates the
number of detonation. The mechanic set the engine condition
depends on the number.

 

[whenfoxforks-ruled]

Not possible in this reality to melt a titanium or stainless exhaust. How do I know? I have jetted a few 450f's and a 250f. The best jetting tip I can give someone with issues, go to extremes on the jetting to feel, see and hear the difference it makes. I have manipulated the color of the header, from dark red to nearly white, all with the pilot jet. Not to mention the 4 foot flames out the exhaust. Plynn 41, best of luck with the high end tuners, but that temperature sensor would be better suited for a 2 stroke. Wide band O2 sensors for 4 strokes. I do not know everything, I have to double check, recheck, and I am still learning. But spewing misinformation is very closely monitored!

 

[plynn41]

Well, I try to learn something every day. Thanks Rich for the lesson.

And right or wrong, I'm sorry Bob for being a jerk to you.

 

[whenfoxforks-ruled]

And I should have checked, and read Rich's post BEFORE typing, again. Thanks Rich, copy and pasting.

 

[knight rider]

would it be wrong of me to say i am confused as hell now. do i mess with the fuel screw now or not?

 

[Rich Rohrich]

The fuel screw is a simple logical first step, and it's a change you can easily undo if it doesn't help. Go for it.

 

[sharky243]

I have an 03' yz 450f, great bike, wouldn't trade it for the world. I've owned it since new and the header glows cherry red within a minute or so of running. It has done this from day one. Stock they have a 12.5:1 compression ratio. This creates alot of heat from the combustion process. What you are experiencing is normal for todays four stroke MX'ers.

 

[whenfoxforks-ruled]

The carb has never been adjusted before? I have had to adjust the mixture screw multiple times a day. I hated the loose fit of the after market screws, but its better than getting burn't! Keep track of adjustments, you can always put it back. And you can flip the choke on to see if it gets lighter, or darker colored. When the carb adjustment is off, it usually does some popping and bogging. If it runs fine, quit looking at the pipe, what Sharky said!

 

[Ol'89r]

would it be wrong of me to say i am confused as hell now. do i mess with the fuel screw now or not?

Like Rich said, try it. See if it makes a difference.

Assuming the water pump is working properly, another way to see if it could be bad valves is to ride the bike. If the glow goes away while riding the bike, that is normal. If the pipe continues to glow while riding the bike, your exhaust valves could be leaking.

When was the last time you checked your valve clearance? Are they the original valves?

If it were my bike, the first thing I would do is try the fuel screw adjustment. Then check the valve clearance. Then do a compression or leak-down test to determine the condition of your rings and valves. The tip-off is your statement that it heats up in 'seconds'. In my experience, this almost always indicates leaky exhaust valves.

 

[pesky nz]

We had this happen once but it we also had lots of backfire /popping and it turned out the carb slide plate was upside down. very carefully and deliberatley look at all parts touched while cleaning out carb, as if this is a new problem it is 99% likely it comes from what you have done inside carb.
Too rich can create a situation where combustion re-occurs inside the exhaust after the exhaust valves open, too rich also can creat bore wash eliminating lubrication to the cylinder both are bad and shorten engine life although the glowing header is a good party trick after dark

 

[pesky nz]

types of detonation

You once asked me for evidence of micro or intermittent
detonation. My interpretation of your post is you have just provided us both with the proof ??
If I'm on the wrong track let me know.

 

[Rich Rohrich]

You once asked me for evidence of micro or intermittent
detonation. My interpretation of your post is you have just provided us both with the proof ??
If I'm on the wrong track let me know.

You're off the track and headed for the weeds. :)

Honda is using knock sensor technologies similar to those being used in the automotive industry, it's just tuned very specifically to the frequency range that will be present in the RS125 and RS250 two-stroke engines.

The Knocking sound you hear when an engine is experiencing abnormal combustion is the result of a rapid pressure rise in the cylinder. Unburned mixture and the end gases at the edges of the combustion chamber are being raised to extremely high temperatures as the advancing flame front compresses and heats up the mixture directly in front of it. This activity before the flame front reaches the end gases at the edge of the chamber are sometimes called pre-flame reactions. The longer it takes for the complete burning to take place the greater the chances that these pre-flame reactions will force the end gases to reach the auto ignition point and cause a rapid uncontrolled pressure rise, along with a huge increase in cylinder temperature. If brought to the auto ignition point the end gases of the combustion chamber can cause a pressure and frequency rise that is high enough to be audible. That's the KNOCK or PING that you hear. Ideally, the burning of the mixture will be completed before any of these end gases have an opportunity to reach the point of auto ignition.


It's important to remember that the air/fuel ratio that produces the best power also tends to have the best chance of knocking. Running on the rich side of best power on a two-stroke tends to cool the piston crown and minimize knock, but go too far and the power drops quickly.

Honda is measuring REAL spark knock aka detonation, not some mythical micro detonation.

In 125 GP roadracing every little bit of power matters. So what Honda is doing is measuring real spark knock, not to stop it completely, but to find the minimum amount of knock that will produce best power and still allow the engine to finish a race.

We tune two-strokes that way at the drag strip. Much like drag racing, pistons are treated as disposable commodities in two-stroke GP racing. Dirt riders have to tune much more conservatively for their application.

As you get comfortable reading plugs, piston crowns, and cylinder heads you can see traces of knock that might not always be heard by a rider. The problem is that can take years to master. Using a device that can detect the number of times a high frequency pressure spike occurs in the combustion chamber is much more reliable than all but the most expert of tuners. Most riders have to just tune to the safe and slow side. Devices like Honda designed can get the average racer closer to an optimized package without the usual learning curve that destroys a lot of parts along the way.

I hope that answered your question. ;)

 

[pesky nz]

seems I'm using some wrong wording, whenever I've read or heard of micro detonation it has been lumped in with inaudible detonation that these knock sensors are made to detect, so I've been incorrectly refering to inaudible as micro.
At trade school we were also told that the detonation knock sound came mostly from the normal flame hitting the auto ignition flame (the colission of 2 flame fronts)
I may also be hearing the wrong thing since what I thought was detonation in my watercooled 250 sounded more like small amounts of sand being digested (after long full throttle period and acompanied by running on into the next 2 corners) than the ping heard next to most yz490

 

[whenfoxforks-ruled]

Ahha, Pesky, welcome to middle age!